Abstract: Deformation of the deposit bank slope is intensified due to reservoir water regulation and rainfall, threatening reservoir operation. To investigate the deformation and failure mechanisms of bank slopes, as well as their infiltration characteristics, a large- scale physical model test was conducted to simulate rainfall and its interactions with water level fluctuations at the Sanbanxi Reservoir in Guizhou Province. The parameters such as pore water pressure in slope and the whole process of slope deformation evolution are obtained. The results show that: (1) The final shape of the modeled wetting front is determined by the slope shape, and the different infiltration effects are mainly manifested in the change of migration depth, and the seepage field characteristics and slope gradient have a greater influence on the migration rate. (2) The soil pressure curve changes gently under both conditions, the pore water pressure changes with a lag, and the soil pressure and pore water pressure in the deeper layers of the slope body fluctuate more than those in the shallower layers in the saturated state. (3) Slope deformation during rainfall is dominated by erosion pits and localized slides, while erosion gullies dominate during coupling, and the scale of slope erosion during coupling is about twice as large as that during rainfall, but multi-stage slip traction damage occurs at the foot of the slopes in both conditions. (4) Based on the experimental results, the deformation and damage mechanism of the modeled bank slope under the coupled rainfall and water level is summarized into five stages: softening and settling of the slope surface, development and expansion of erosion rills, and development of erosion gullies and collapse at the foot of the slope. The results of this study fill the gap in the study of bank slope stability under the above conditions in Sanbanxi Reservoir area, and it is useful for the study of similar deformation damage of gravel soil bank slopes and their prevention and control.

Key words: rainfall and reservoir water level, gravel soil bank slope, model test, deformation and failure mechanism, infiltration features